1. Field of the Invention
The present invention relates generally to compressors, and more particularly, but not by way of limitation, to an improved monoblock gas compressor having a compressor head for safely containing supply gas having a pressure above atmospheric pressure and adaptable for multiple-stage compression.
2. Brief Description of the Related Art
The use of internal combustion engines which have had a portion thereof converted for use as a gas compressor is well known. Such compressors are known as monoblock compressors in that one engine cylinder block is utilized for both power and air compression. V-6 and V-8 engines are the engines most commonly used for a monoblock compressor with one bank of cylinders being used for power and the other bank of cylinders being used for compression. The engine is converted for compression by replacing the standard cylinder head and valve cover with a compressor head which is provided with a compressor valve so as to permit air to be sucked into the cylinder bore on the down stroke of the piston and compressed and discharged on the up stroke of the piston.
Monoblock compressors designed for compressing air do not require any type of sealed intake manifold due to the fact that the supply air is at atmospheric pressure. In contrast, when the pressure of the supply gas is greater than atmospheric pressure, the inlets to the compressor valves must be sealed. For example, natural gas produced from subterranean formations is generally at pressures greater than atmospheric pressure. Nevertheless, a compressor must often be employed to further compress the natural gas to facilitate its delivery to a gas gathering network.
A monoblock compressor for use with natural gas is disclosed in U.S. Pat. No. 4,961,691, issued to Waldrop. Waldrop discloses a monoblock gas compressor having an inlet manifold connected to a compressor head. The inlet manifold is provided with a pair of gas inlets and is adapted to cover the top of the compressor head in a manner similar to a conventional valve cover. A seal member, such as an O-ring or a gasket, is positioned between the inlet manifold and the compressor head to provide sealing engagement between the inlet manifold and the compressor head. The problem encountered is that the seal member is generally rated for pressures of 10-20 psig. Consequently, when utilizing the monoblock compressor of Waldrop, natural gas producers are limited in the pressure at which they can supply the natural gas to the compressor without fear of blowing out the seal member and having gas leak from the compressor and potentially being ignited by a spark from the engine or some other source. Gas can also leak past the seal member upon the seal member becoming worn or damaged. To this end, a need exists for an improved monoblock compressor having a compressor head for safely containing supply gas having a pressure above atmospheric pressure.
In addition, it is sometimes necessary to compress gas in multiple stages to obtain higher discharge pressures. In the past, multiple stage compression has required the use of a separate compressor for each stage of compression. In the case of using monoblock compressors for multiple stage compression, this results in an increase in equipment cost of two to three fold depending on the number of compression stages, as well as an increase in the cost of operating each of the compressors. Thus, a need also exists for a compressor head that is adaptable for multiple stage compression.